The generation of a current of spin-polarised electrons, in which all electron spins point mostly in the same direction, is a central aspect of spin electronics (hereafter also called spintronics). Spintronics, or spin electronics, refers to the role played by electron spin in solid state physics, and to devices that specifically exploit spin properties, i.e. spin degrees of freedom, instead of, or in addition to, charge degrees of freedom. For example, spin relaxation and spin transport in metals and semiconductors are of interest in fundamental research such as solid state physics and more generally in other electronic technology areas. Extensive research and development is carried out in the field of spintronics with the objective to fully utilise the advantage that no electron charges need to be transported which would cost energy and produce heat.
To date, currents of spin-polarised electrons are predominantly obtained from magnetic or magnetized materials. When the spin has to be inverted the applied external magnetic field needs to be inverted. This is typically intrinsically slow to carry out, and would thus be inefficient for many applications.
Furthermore, currents of spin-polarised electrons can be obtained when circularly polarised light ejects electrons from substrates with large spin-orbit coupling, for example gallium arsenide (GaAs).
In the above mentioned methods, the materials used are prepared in complex preparations under ultra-high vacuum (UHV) conditions. Thus, their integration into large scale integrated circuits or even printed circuits is difficult.
An important attribute of free spin-polarised electrons is the degree of polarisation. The degree of polarisation of free spin-polarised electrons is presently measured by so called Mott scattering of high energy electrons on thin gold foil under high vacuum conditions. The high energy electrons are in the region of more than 50 kV and the thin gold foil is in the region of a few nanometers. Alternatively, the degree of polarisation of free spin-polarised electrons can be measured by spin-dependent diffraction at surfaces of wolfram (W) or iron (Fe) under ultra-high vacuum conditions (less than 10−10 mbar). However, both methods for detecting spin-polarised electrons are technically complex and prone to errors.